1. Field of the Invention
The present invention relates to a brightness control apparatus, a display apparatus including the brightness control apparatus, and a lighting apparatus including the brightness control apparatus. More particularly, the present invention relates to a brightness control apparatus, a display apparatus including the brightness control apparatus, and a lighting apparatus including the brightness control apparatus for performing stable brightness control for backlights of the display apparatus and the lighting apparatus.
2. Description of the Related Art
In technical fields of various display apparatuses for displaying pictures or images, enhancement of image quality and improvement of power consumption and the like are being studied. Also, as recent display apparatuses, especially, liquid crystal displays (LCD) are commonly used.
In general, the LCD is configured to include an output panel for displaying an image using light and a backlight unit for emitting light. The backlight unit is designed mainly for the purpose of providing light evenly to an effective display area of the output panel on which the image is displayed.
Also, control apparatuses (for example, contents analyzer) for controlling the backlight unit are known. Generally, in these control apparatuses, backlight control is performed by using simple APL (Average Picture Level (average brightness level)) detection. Also, it is known that brightness control is performed linearly using APL information of an image signal when controlling brightness of backlights of the LCD panel.
In recent years, techniques for using plural light-emitting elements such as LED (Light Emitting Diode) as backlight or lighting are attracting attention. In the LEDs, LED-by-LED variation occurs. As the variation of LEDs, it is known that there are variations in a steady state, variation due to temperature change and variation due to temporal change and the like. The variations in a steady state include manufacturing variations at a component level. It is left up to user's decision whether to select a product or to use a production without selection, which largely influences the price of the product. Several techniques for the variations are disclosed (refer to patent documents 1: Japanese Laid-open patent application No. 2006-31977 and patent documents 2:Japanese Laid-open patent application No. 11-305198, for example).
The patent document 1 discloses a backlight apparatus including a lighting unit having plural light-emitting diodes, a driving unit for driving light-emitting diodes, and a temperature detection unit. The driving unit adjusts currents supplied for the light-emitting diodes according to a temperature of the lighting unit. The patent document 2 discloses a liquid crystal display apparatus for driving LED backlights using a constant-current circuit.
As mentioned above, there are plural types of LED variations such as the steady-state variation, temperature-change variation, and temporal-change variation. Therefore, it is necessary to perform brightness control against brightness variation using a proper method for each of the types. However, such a technique has not been proposed.